The answer

Oilseed rape prices have risen dramatically

Harvests in rest of Europe have been disrupted by bad weather

Dr Fiona Burnett, a plant pathologist at the Scottish Agricultural College, says rapeseed oil has historically fulfilled a useful role as a "break crop" in farm rotation - to suppress weeds and improve soil quality - for cereal crops such as wheat and barley.

But whereas in the past the crop has been largely functional - and has not made farmers much money - in recent years it has become hugely profitable, she says.

"Forward prices for the current crop are as high as £388 per tonne, which compares to £240 in 2010, which is a huge rise in profitability."

When compared with the profit on other break crops such as beans, "using rapeseed oil is a no-brainer", she adds.

Burnett says around 698,000 hectares in England and Wales and around 37,000 hectares in Scotland have been sown with oilseed rape this year, up about 6% on last year, according to the Home Grown Cereal association survey.

It is easy to see why farmers would change to crops that fill their pockets, but what is driving demand?

Guy Gagen, chief arable adviser at the National Farmers Union, says rapeseed oil is actually one of the highest quality vegetable oils, and it has gained a certain culinary respectability over recent years.

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"It's being used as mayonnaise, in margarine, salads, anywhere vegetables are used. It has a good health profile, has low saturated fat, is high in omega-3, and some claim it is better than sunflower oil," he says.

The oil also has some high profile fans, with chefs James Martin and Hugh Fearnley-Whittingstall said to be converts to the rapeseed revolution.

The UK's "consistently high yields" of rapeseed have made the crop a success, according to Gagen.

"Our rape crops are in extremely good condition. Other places like Germany, Poland and Ukraine have had a dreadful winter, the crops were exposed to severe cold temperatures, I suspect the French suffered as well.

"Rapeseed oil is one of the highest yield oils - it has very black seeds, which are like poppy seeds, and they are 45% oil - and the other 55% is high protein animal feed - they are an amazing piece of nature," he says.

Burnett says oilseed rape is also being used for biodiesel, while a very small amount has specialist industrial uses, for instance as lubricants.

There is also a rise in "quality" markets - with "cold pressed" oils such as Glendaveny, Ola Oils and Border Fields on the rise, she adds.

Of course, economics and nutrition aside, it's not to everybody's taste on a purely aesthetic basis.

For some, endless fields of yellow disrupt traditional British landscapes.

However fans of England's green and pleasant land should not despair. Burnett says oilseed rape has probably been more visible this year because it has flowered for almost twice its normal length of time - eight weeks, instead of four - as a cold and wet April and May stopped flowers developing and dying at their normal rate.

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